Method and apparatus for sealing thin metal members to glass envelopes



Oct. 21, 1930.

E. F. GATES 1,779,311 METHOD AND APPARATUS FOR SEALING THIN METAL MEMBERS TO GLASS ENVELOPES Filed Oct. 17, 1929 Fig.2.

Inventor: Edwin F. Gates by WM His Attorney.

Patented Oct. 21, 1930 UNITED STATES PATENT OFFICE EDWIN l. GA'I'EB, OI SCOTIA, NEW YORK, ABSIGHOB 130 GENERAL ELECTRIC 001mm, A OOBPOBATIONOI' HEW You IETHOD AND APPARATUS FOR SEALING THIN METAL MEMBERS TO GLASS ENVELOPE Application fled October 17, 1928. Serial No. 400,421.

The present invention relates to the art of joining metal to glass and more particularly to the method of and apparatus for sealing thin metal pieces to lass envelopes.

In the arts, there frequently arises the necessity of forming a hermetic seal between the thin metal member and the glass envelope, for example in an X-ray apparatus it may be desired to abricate a tube to generate X- rays of relatively low intensity for articuular kinds of radiographic work an calling for a window of thin material in order not to absorb the rays to an appreciable extent. If thin glass be employed for the window it tends to fracture easily. On the other hand, when metal is used, the window is much tougher and can stand harder usage, and besides, may be rolled to a definite and uniform thickness but there are involved difiiculties of construction. One diflicult is in forming the seal around the metal; the heat from the sealing torch may warp or otherwise deform the metal member, thus introducing strains and leakage at the sealing edge as well as offerin different thicknesses of metal for the rays to traverse, and under extremely adverse conditions the torch may actually melt and destroy the window. When the window contains deformations of the surface, e. g. corrugations, the rays are absorbed in a variable manner over the window area and variations are roduced in the X-ray output.

Objects of t e invention are to provide an improved method of constructingX-ray tubes having a metal window whereby the disadvantages attending this form of window are obviated and, in general, to improve the technique of hermetically sealing thin metal sheets to glass, requiring the minimum apparatus and labor. Other objects and features will be apparent as the specification is perused in connection with the accompanying drawing in which Fig. 1 illustrates a side view in perspective of an X-ray tube provided with a metal window sealed in the improved manner; Fig. 2 represents one step in the improved method of sealing, together with the a paratus for erforming the method; while igs. 3 and 4 i ustrate further steps and apparatus.

Referring to Fi 1, numeral 1 designates an evacuated enve ope containing the usual electrodes for producin X-rays, 1. e. a tungsten copper-backed ano e or a target 2 and a combined cathode or ray-focusing arrangement 3. The electrodes may be secured in any suitable manner to the reentrant stems 4, 4 which are disposed normal to each other. X rays of relatively low penetrating power may be produced at the target by accelerating the electrons through a suitable otential gradient, for example, of the order of 4,000 to 10,000 volts and directed through a metal window 5. The window may be constituted of a chrome-iron alloy, commonl called in the arts Ascolo or other suitab e material and in order to a lowthe rays facility of traverse, 1. e. without undue absorption, the metal must be exceedingly thin, for example, of the order of .5 mil.

It has heretofore been considered impossible to seal a window of this kind into a glass envelope but in accordance with the resent invention the technique of construction has been improved to such an extent that not only is a perfect seal obtained, but also the metal remains flat in position. The first ste in the improved method is to cause a sealin eador layer 5' of glass, 5 from a preferably applie cane 6 by means 0 a torch 7, to adhere about the peripheral edge of the window 5. A glass known as French lead glass is suitable for this purpose. During this operation the window is held rigidly between two metal members 8, 9 shown in the form of cylinders and provided with flat abutting faces. The cylinders are clamped about the window 5 in any suitable manner, for example, by means of a flexible wire member 10 which is afiixed at the lower end to a cylinder 9 and at the upper end projects into a counter-sink 11 formed on the top surface of the cylinder 8. The upper cylinder may be removed to break the clamp by simply forcingthe spring member out of the counter-sink.

The next step is to seal the window in the glass envelope and this is accomplished preferably in a machine or attachment therefor adapted to rotate the envelope as shown in Fig 4. The window is afiixed in place preferably before the reentrant stems 4 are sealed to the envelope, the openings in the latter provided for the stems being tem rarily closed by lugs 12, 13 of cork, ru her or the like. The attachment consists in part of a shaft constituted of several ortions, described hereinafter, which is a apted to revolve in ball bearin 14 by means of a pulle 15 and a power driven belt 16. The sha comprises a su port rod 17 and a clamping device 18, 19 w lch has a function similar to that described in connection with Fig. 2. The support rod 17 is maintained in central ah?- ment within one arm of the envelope 1 y means of a centering ring 20 of cork or rubher and also by passin tightly throu h a central opening in the p ug 12. The ro terminates in a screw 21 and 1s hollow throughout its length except for a wall of metal left at the screw end; in other words, the rod may constitute a heavy tubing plugged at one end and fitted with a screw ortion at the plugged end. There are a num er of holes 22 drilled through the material of the rod and equi-distantly spaced about the tubing at the closed end; the purpose of the holes will be explained presently. The lower clamp member 19 is secured by the screw 21 while the upper clamp member 18 is held in place by an overhanging structure which is secured to the rod 17 by means of an arm 24 and a set screw 25. The arm 24 has an opening at its lower end into which is tight] fitted an u right tubular member 26 provi ed at each on with flanges 27. Within the tube 26, there is slidably arranged a rod 28 which terminates at the lower end in a flange 29 and at the upper end is fitted into a horizontally dispose ar 30. The latter is rigidly afilxed to the upper clamp member 18 in any suitable manner, for example, by screw 31. Between the lower flange 27 and flange 29, there is positioned a compression spring 32 which tends to force the flanges apart, thereby causing the member 18 to press against the juxta osed member 19 with a force sufliciently rigid to hold the window 4 between the flat surfaces. In the sealing operation, the envelope 1 is so positioned on the composite shaft, i. e. by adjusting the tube 17 within the plug 12 that the window 5 to which the glass head has already been applied, when held between the clamp members, rests upon the o ening in the envelope, as shown in Fig. 3. The 0 ening is of a size large enough to allgw the g ass bead to contact with the envelope, thereby providing a glass to glass seal at this point. torch 33 may be applied to the joint and at the same time the shaft turned rather slowly by the belt 16 until the two glass portions are hermetically sealed or fused in a uniform manner. In order to prevent any deformation or collapse of the envelo e at the place where the heat is applied a b ast of air may be blown, conveniently by the mouth of the aside.

operator, into the lower end of the tube 17 at the lace indicated on the drawing, the air passing through the apertures 22 to maintain a pressure against the interior surface of the envelope. When the seal has been completed the rotation of the envelope is stopped an the upper clamp member 18 raise against the compression of the sprin 32 and swun he plug 12 may now loosened an ,the envelope withdrawn by moving it in an upward direction in which case the envelope leaves the lower plug and may be slipped over the member 20. The plug 13 is thereupon removed and the envelope is ready to have the reentrant stems and electrodes sealed in place in the usual manner.

It will be noted that the clamping members 8 and 9 in the prcliminar operation of the members 18 and 19 in the nal sealing operation serve not only rigidly to hold the window absolutely flat in its proper position but also to provide a mechanical barrier for preventing the torch flame from reaching the metal except at the sealing ed e and in addition, to provide a large mass 0 metal to absorb and istribute the excess heat generated at the point of the seal. The metal window of minute thickness is thus efi'ectivel sealed without the danger of being either eformed or destroyed liy the heatutilized in the sealing recess. t is'apparnt'tliat the position -of t e window with respect-to the envelope may readily be adjusted in the clamp arran ement to give any desired orientation or position and that the clamping ieces may be given a configuration to con orm to any sha e of 'window. It will also occur to those skil ed in the art that a single set of clamping members if desired, may be utilized for both the preliminary and final sealin oper ations and the apparatus simplified urther to that extent.

What I claim as new and desire to secure by Letters Patent of the United States, is,-

1. In the method of sealing a thin, flat metal member to a glass body, the ste s of clamping the member between two fiat, eatconducting surfaces, then applying a layer of glass to the sealing edge of said member, fifiallly fusing the glass sealing edge to the glass 2. In the art of sealing a thin, metal window to the glass envelope of an X-ray tube, the method which consists in clamping the window between two plate surfaces, then. applying a layer of glass to the scaling edge A of the window, then positionin the window on the envelo e, finally sealin t e window to the envelope y heating the 'oint between the layer of glass and the envelope while maintaining a flat, clamping surface on each side of the window.

3. Apparatus for sealing a thin, flat metal member to a glass body comprising a pair of elements of heat conducting material adapted to be clamped about said metal member and provided with flat clamping surfaces, said elements being of a size suflielent to cover the metal member except at the portion which is to be sealed to the glass body.

4. Apparatus for sealing a thin, flat metal member to a glass envelope comprising-a pair of metallic elements adapted to be clamped about said metal member and provided with flat clamping surfaces, said members being of a size suflicient to cover the metal member except at the portion which is to be sealed to the glass envelope, and means for rotating the clamping elements during the sealing operation.

In witness whereof, I have hereunto set my hand this 16th day of October, 1929.

EDWIN F. GATES.

ed to be clamped about said metal member and provided with flat clamping surfaces, said elements being of a size suificlent to cover the metal member except at the portion which is to be sealed to the glass body.

4. Apparatus for sealing a thin, flat metal member to a glass envelope comprising a pair of metallic elements adapted to be clamped about said metal member and provided with flat clamping surfaces, said members being of a size sufi'icient to cover the metal member except at the portion which is to be sealed to the glass envelope, and means for rotating the clamping elements during the sealing operation.

In witness whereof, I have hereunto set my hand this 16th day of October, 1929.

EDWIN F. GATES.

cmmcm or common.

Patent No. 1,779,311.

Granted October 21, 1930, to

EDWIN F. GATES.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Page 2, line 120, claim 2, for the word "plate" read flat; and that the said Letters Patent should he read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 9th day of December, A. D. 1930.

(Seal) M. J. Moore, Acting Commissioner of Patents.

CERTIFICATE OF CORRECTION.

Patent No. 1,779,311. Granted October 21, 1930, to

EDWIN F. GATES.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, line 120, claim 2, for the word "plate" read flat; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 9th day of December, A. D. 1930.

M. J. Moore,

(Seal) Acting Commissioner of Patents. 

